Chapter 14. Integrating view technologies

14.1. Introduction

One of the areas in which Spring excels is in the separation of view
technologies from the rest of the MVC framework. For example, deciding to
use Velocity or XSLT in place of an existing JSP is primarily a matter of
configuration. This chapter covers the major view technologies that work
with Spring and touches briefly on how to add new ones. This chapter
assumes you are already familiar with Section 13.5, “Views and resolving them”
which covers the basics of how views in general are coupled to the MVC
framework.

14.2. JSP & JSTL

Spring provides a couple of out-of-the-box solutions for JSP and
JSTL views. Using JSP or JSTL is done using a normal view resolver defined
in the WebApplicationContext. Furthermore,
of course you need to write some JSPs that will actually render the view.

14.2.1. View resolvers

Just as with any other view technology you're integrating with
Spring, for JSPs you'll need a view resolver that will resolve your
views. The most commonly used view resolvers when developing with JSPs
are the InternalResourceViewResolver and the
ResourceBundleViewResolver. Both are declared in the
WebApplicationContext:

As you can see, the ResourceBundleViewResolver needs
a properties file defining the view names mapped to 1) a class and 2) a URL. With a
ResourceBundleViewResolver you can mix different types of views using
only one resolver.

The InternalResourceBundleViewResolver can be configured for using
JSPs as described above. As a best practice, we strongly encourage
placing your JSP files in a directory under the 'WEB-INF' directory, so
there can be no direct access by clients.

14.2.2. 'Plain-old' JSPs versus JSTL

When using the Java Standard Tag Library you must use a special view
class, the JstlView, as JSTL needs some preparation
before things such as the i18N features will work.

14.2.3. Additional tags facilitating development

Spring provides data binding of request parameters to command
objects as described in earlier chapters. To facilitate the development
of JSP pages in combination with those data binding features, Spring
provides a few tags that make things even easier. All Spring tags have
html escaping features to enable or disable
escaping of characters.

The tag library descriptor (TLD) is included in the
spring.jar as well in the distribution itself.
Further information about the individual tags can be found in the appendix entitled
Appendix D, spring.tld.

14.3. Tiles

It is possible to integrate Tiles - just as any other view
technology - in web applications using Spring. The following describes in
a broad way how to do this.

NOTE: Spring 2.0 supports Tiles 1.x (a.k.a. "Struts Tiles",
as shipped with Struts 1.1+). There is no out of the box support for Tiles 2 yet.

14.3.1. Dependencies

To be able to use Tiles you have to have a couple of additional
dependencies included in your project. The following is the list of
dependencies you need.

Struts version 1.1 or higher

Commons BeanUtils

Commons Digester

Commons Logging

These dependencies are all available in the Spring distribution.

14.3.2. How to integrate Tiles

To be able to use Tiles, you have to configure it using files
containing definitions (for basic information on definitions and other
Tiles concepts, please have a look at http://struts.apache.org). In Spring this is done
using the TilesConfigurer. Have a look at the
following piece of example ApplicationContext configuration:

As you can see, there are five files containing definitions, which
are all located in the 'WEB-INF/defs' directory.
At initialization of the WebApplicationContext,
the files will be loaded and the definitions factory will be initialized.
After that has been done, the Tiles includes in the definition files can be used
as views within your Spring web application. To be able to use the views
you have to have a ViewResolver just as with any
other view technology used with Spring. Below you can find two
possibilities, the UrlBasedViewResolver and
the ResourceBundleViewResolver.

14.3.2.1. UrlBasedViewResolver

The UrlBasedViewResolver instantiates the given
viewClass for each view it has to resolve.

...
welcomeView.class=org.springframework.web.servlet.view.tiles.TilesView
welcomeView.url=welcome (this is the name of a Tiles definition)
vetsView.class=org.springframework.web.servlet.view.tiles.TilesView
vetsView.url=vetsView (again, this is the name of a Tiles definition)
findOwnersForm.class=org.springframework.web.servlet.view.JstlView
findOwnersForm.url=/WEB-INF/jsp/findOwners.jsp
...

As you can see, when using the ResourceBundleViewResolver,
you can easily mix different view technologies.

Note that the TilesView class does not
support JSTL (the JSP Standard Tag Library) out of the box. There is a separate
TilesJstlView subclass for JSTL-enabled templates.

14.4. Velocity & FreeMarker

Velocity and
FreeMarker are two
templating languages that can both be used as view technologies within
Spring MVC applications. The languages are quite similar and serve similar
needs and so are considered together in this section. For semantic and
syntactic differences between the two languages, see the FreeMarker web site.

14.4.1. Dependencies

Your web application will need to include
velocity-1.x.x.jar or
freemarker-2.x.jar in order to
work with Velocity or FreeMarker respectively and
commons-collections.jar
needs also to be available for Velocity. Typically they are included in
the WEB-INF/lib folder where they are guaranteed to
be found by a J2EE server and added to the classpath for your
application. It is of course assumed that you already have the
spring.jar in your
'WEB-INF/lib' directory too!
The latest stable velocity, freemarker and commons
collections jars are supplied with the Spring framework and can be
copied from the relevant /lib/
sub-directories. If you make use of Spring's dateToolAttribute or
numberToolAttribute in your Velocity views, you will also need to include the
velocity-tools-generic-1.x.jar

14.4.2. Context configuration

A suitable configuration is initialized by adding the relevant
configurer bean definition to your '*-servlet.xml' as shown below:

<!--
This bean sets up the Velocity environment for us based on a root path for templates.
Optionally, a properties file can be specified for more control over the Velocity
environment, but the defaults are pretty sane for file based template loading.
-->
<bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer">
<property name="resourceLoaderPath" value="/WEB-INF/velocity/"/>
</bean>
<!--
View resolvers can also be configured with ResourceBundles or XML files. If you need
different view resolving based on Locale, you have to use the resource bundle resolver.
-->
<bean id="viewResolver" class="org.springframework.web.servlet.view.velocity.VelocityViewResolver">
<property name="cache" value="true"/>
<property name="prefix" value=""/>
<property name="suffix" value=".vm"/>
<!-- if you want to use the Spring Velocity macros, set this property to true -->
<property name="exposeSpringMacroHelpers" value="true"/>
</bean>

<!-- freemarker config -->
<bean id="freemarkerConfig" class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer">
<property name="templateLoaderPath" value="/WEB-INF/freemarker/"/>
</bean>
<!--
View resolvers can also be configured with ResourceBundles or XML files. If you need
different view resolving based on Locale, you have to use the resource bundle resolver.
-->
<bean id="viewResolver" class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver">
<property name="cache" value="true"/>
<property name="prefix" value=""/>
<property name="suffix" value=".ftl"/>
<!-- if you want to use the Spring FreeMarker macros, set this property to true -->
<property name="exposeSpringMacroHelpers" value="true"/>
</bean>

Note

For non web-apps add a VelocityConfigurationFactoryBean or a
FreeMarkerConfigurationFactoryBean to your application context definition file.

14.4.3. Creating templates

Your templates need to be stored in the directory specified by the
*Configurer bean shown above. This document does not cover
details of creating templates for the two languages - please see their
relevant websites for information. If you use the view resolvers
highlighted, then the logical view names relate to the template file
names in similar fashion to
InternalResourceViewResolver for JSP's. So if your
controller returns a ModelAndView object containing a view name of
"welcome" then the resolvers will look for the
/WEB-INF/freemarker/welcome.ftl or
/WEB-INF/velocity/welcome.vm template as
appropriate.

14.4.4. Advanced configuration

The basic configurations highlighted above will be suitable for
most application requirements, however additional configuration options
are available for when unusual or advanced requirements dictate.

14.4.4.1. velocity.properties

This file is completely optional, but if specified, contains the
values that are passed to the Velocity runtime in order to configure
velocity itself. Only required for advanced configurations, if you
need this file, specify its location on the
VelocityConfigurer bean definition above.

Refer to the API
documentation for Spring configuration of Velocity, or the
Velocity documentation for examples and definitions of the
'velocity.properties' file itself.

14.4.4.2. FreeMarker

FreeMarker 'Settings' and 'SharedVariables' can be passed
directly to the FreeMarker Configuration object
managed by Spring by setting the appropriate bean properties on the
FreeMarkerConfigurer bean. The
freemarkerSettings property requires a
java.util.Properties object and the
freemarkerVariables property requires a
java.util.Map.

See the FreeMarker documentation for details of settings and
variables as they apply to the Configuration
object.

14.4.5. Bind support and form handling

Spring provides a tag library for use in JSP's that contains
(amongst other things) a <spring:bind/> tag.
This tag primarily enables forms to display values from form backing
objects and to show the results of failed validations from a
Validator in the web or business tier. From version
1.1, Spring now has support for the same functionality in both Velocity
and FreeMarker, with additional convenience macros for generating form
input elements themselves.

14.4.5.1. The bind macros

A standard set of macros are maintained within the
spring.jar file for both languages, so they are
always available to a suitably configured application. However they
can only be used if your view sets the bean property
exposeSpringMacroHelpers to 'true'
on your VelocityView / FreeMarkerView
beans. By way of a shortcut, you can also configure this property on
VelocityViewResolver or
FreeMarkerViewResolver too if you happen to be
using it, in which case all of your views will inherit the value from
it. Note that this property is not
required for any aspect of HTML form handling except where you wish to take advantage of the
Spring macros. Below is an example of a view.properties file showing
correct configuration of such a view for either language;

Some of the macros defined in the Spring libraries are
considered internal (private) but no such scoping exists in the macro
definitions making all macros visible to calling code and user
templates. The following sections concentrate only on the macros you
need to be directly calling from within your templates. If you wish to
view the macro code directly, the files are called spring.vm /
spring.ftl and are in the packages
org.springframework.web.servlet.view.velocity or
org.springframework.web.servlet.view.freemarker
respectively.

14.4.5.2. simple binding

In your html forms (vm / ftl templates) that act as the
'formView' for a Spring form controller, you can use code similar to
the following to bind to field values and display error messages for
each input field in similar fashion to the JSP equivalent. Note that
the name of the command object is "command" by default, but can be
overridden in your MVC configuration by setting the 'commandName' bean
property on your form controller. Example code is shown below for the
personFormV and personFormF
views configured earlier;

#springBind /
<@spring.bind> requires a 'path' argument
which consists of the name of your command object (it will be
'command' unless you changed it in your FormController properties)
followed by a period and the name of the field on the command object
you wish to bind to. Nested fields can be used too such as
"command.address.street". The bind macro assumes
the default HTML escaping behavior specified by the ServletContext
parameter defaultHtmlEscape in web.xml

The optional form of the macro called
#springBindEscaped /
<@spring.bindEscaped> takes a second argument
and explicitly specifies whether HTML escaping should be used in the
status error messages or values. Set to true or false as required.
Additional form handling macros simplify the use of HTML escaping and
these macros should be used wherever possible. They are explained in
the next section.

14.4.5.3. form input generation macros

Additional convenience macros for both languages simplify both
binding and form generation (including validation error display). It
is never necessary to use these macros to generate form input fields,
and they can be mixed and matched with simple HTML or calls direct to
the spring bind macros highlighted previously.

The following table of available macros show the VTL and FTL
definitions and the parameter list that each takes.

Table 14.1. Table of macro definitions

macro

VTL definition

FTL definition

message (output a
string from a resource bundle based on the code
parameter)

#springMessage($code)

<@spring.message
code/>

messageText (output a
string from a resource bundle based on the code parameter,
falling back to the value of the default parameter)

#springMessageText($code
$text)

<@spring.messageText code,
text/>

url (prefix a relative
URL with the application's context root)

#springUrl($relativeUrl)

<@spring.url
relativeUrl/>

formInput (standard
input field for gathering user input)

#springFormInput($path
$attributes)

<@spring.formInput path, attributes,
fieldType/>

formHiddenInput *
(hidden input field for submitting non-user input)

#springFormHiddenInput($path
$attributes)

<@spring.formHiddenInput path,
attributes/>

formPasswordInput *
(standard input field for gathering passwords. Note that no
value will ever be populated in fields of this type)

formSingleSelect (drop
down box of options allowing a single required value to be
selected)

#springFormSingleSelect( $path $options
$attributes)

<@spring.formSingleSelect path, options,
attributes/>

formMultiSelect (a
list box of options allowing the user to select 0 or more
values)

#springFormMultiSelect($path $options
$attributes)

<@spring.formMultiSelect path, options,
attributes/>

formRadioButtons (a
set of radio buttons allowing a single selection to be made
from the available choices)

#springFormRadioButtons($path $options
$separator $attributes)

<@spring.formRadioButtons path, options
separator, attributes/>

formCheckboxes (a set
of checkboxes allowing 0 or more values to be
selected)

#springFormCheckboxes($path $options
$separator $attributes)

<@spring.formCheckboxes path, options,
separator, attributes/>

showErrors (simplify
display of validation errors for the bound field)

#springShowErrors($separator
$classOrStyle)

<@spring.showErrors separator,
classOrStyle/>

* In FTL (FreeMarker), these two macros are not actually
required as you can use the normal formInput macro,
specifying 'hidden' or
'password' as the value for the
fieldType parameter.

The parameters to any of the above macros have consistent
meanings:

path: the name of the field to bind to (ie
"command.name")

options: a Map of all the available values that can be
selected from in the input field. The keys to the map represent
the values that will be POSTed back from the form and bound to the
command object. Map objects stored against the keys are the labels
displayed on the form to the user and may be different from the
corresponding values posted back by the form. Usually such a map
is supplied as reference data by the controller. Any Map
implementation can be used depending on required behavior. For
strictly sorted maps, a SortedMap such as a
TreeMap with a suitable Comparator may be used
and for arbitrary Maps that should return values in insertion
order, use a LinkedHashMap or a
LinkedMap from commons-collections.

separator: where multiple options are available as discreet
elements (radio buttons or checkboxes), the sequence of characters
used to separate each one in the list (ie "<br>").

attributes: an additional string of arbitrary tags or text
to be included within the HTML tag itself. This string is echoed
literally by the macro. For example, in a textarea field you may
supply attributes as 'rows="5" cols="60"' or you could pass style
information such as 'style="border:1px solid silver"'.

classOrStyle: for the showErrors macro, the name of the CSS
class that the span tag wrapping each error will use. If no
information is supplied (or the value is empty) then the errors
will be wrapped in <b></b> tags.

Examples of the macros are outlined below some in FTL and some
in VTL. Where usage differences exist between the two languages, they
are explained in the notes.

14.4.5.3.1. Input Fields

<!-- the Name field example from above using form macros in VTL -->
...
Name:
#springFormInput("command.name" "")<br>
#springShowErrors("<br>" "")<br>

The formInput macro takes the path parameter (command.name)
and an additional attributes parameter which is empty in the example
above. The macro, along with all other form generation macros,
performs an implicit spring bind on the path parameter. The binding
remains valid until a new bind occurs so the showErrors macro
doesn't need to pass the path parameter again - it simply operates
on whichever field a bind was last created for.

The showErrors macro takes a separator parameter (the
characters that will be used to separate multiple errors on a given
field) and also accepts a second parameter, this time a class name
or style attribute. Note that FreeMarker is able to specify default
values for the attributes parameter, unlike Velocity, and the two
macro calls above could be expressed as follows in FTL:

<@spring.formInput "command.name"/>
<@spring.showErrors "<br>"/>

Output is shown below of the form fragment generating the name
field, and displaying a validation error after the form was
submitted with no value in the field. Validation occurs through
Spring's Validation framework.

The formTextarea macro works the same way as the formInput
macro and accepts the same parameter list. Commonly, the second
parameter (attributes) will be used to pass style information or
rows and cols attributes for the textarea.

14.4.5.3.2. Selection Fields

Four selection field macros can be used to generate common UI
value selection inputs in your HTML forms.

formSingleSelect

formMultiSelect

formRadioButtons

formCheckboxes

Each of the four macros accepts a Map of options containing
the value for the form field, and the label corresponding to that
value. The value and the label can be the same.

An example of radio buttons in FTL is below. The form backing
object specifies a default value of 'London' for this field and so
no validation is necessary. When the form is rendered, the entire
list of cities to choose from is supplied as reference data in the
model under the name 'cityMap'.

This renders a line of radio buttons, one for each value in
cityMap using the separator "". No additional
attributes are supplied (the last parameter to the macro is
missing). The cityMap uses the same String for each key-value pair
in the map. The map's keys are what the form actually submits as
POSTed request parameters, map values are the labels that the user
sees. In the example above, given a list of three well known cities
and a default value in the form backing object, the HTML would
be

14.4.5.4. HTML escaping and XHTML compliance

Default usage of the form macros above will result in HTML tags
that are HTML 4.01 compliant and that use the default value for HTML
escaping defined in your web.xml as used by Spring's bind support. In
order to make the tags XHTML compliant or to override the default HTML
escaping value, you can specify two variables in your template (or in
your model where they will be visible to your templates). The
advantage of specifying them in the templates is that they can be
changed to different values later in the template processing to
provide different behavior for different fields in your form.

To switch to XHTML compliance for your tags, specify a value of
'true' for a model/context variable named xhtmlCompliant:

Any tags generated by the Spring macros will now be XHTML
compliant after processing this directive.

In similar fashion, HTML escaping can be specified per
field:

<#-- until this point, default HTML escaping is used -->
<#assign htmlEscape = true in spring>
<#-- next field will use HTML escaping -->
<@spring.formInput "command.name" />
<#assign htmlEscape = false in spring>
<#-- all future fields will be bound with HTML escaping off -->

14.5. XSLT

XSLT is a transformation language for XML and is popular as a view
technology within web applications. XSLT can be a good choice as a view
technology if your application naturally deals with XML, or if your model
can easily be converted to XML. The following section shows how to produce
an XML document as model data and have it transformed with XSLT in a
Spring Web MVC application.

14.5.1. My First Words

This example is a trivial Spring application that creates a list
of words in the Controller and adds them to the model
map. The map is returned along with the view name of our XSLT view. See the section
entitled Section 13.3, “Controllers” for details of Spring Web MVC's
Controller interface. The XSLT view will turn the list of
words into a simple XML document ready for transformation.

14.5.1.1. Bean definitions

Configuration is standard for a simple Spring application. The
dispatcher servlet config file contains a reference to a
ViewResolver, URL mappings and a single controller
bean...

<bean id="homeController"class="xslt.HomeController"/>

... that encapsulates our word generation logic.

14.5.1.2. Standard MVC controller code

The controller logic is encapsulated in a subclass of
AbstractController, with the handler method being defined like so...

So far we've done nothing that's XSLT specific. The model data
has been created in the same way as you would for any other Spring MVC
application. Depending on the configuration of the application now,
that list of words could be rendered by JSP/JSTL by having them added
as request attributes, or they could be handled by Velocity by adding
the object to the VelocityContext. In
order to have XSLT render them, they of course have to be converted into
an XML document somehow.
There are software packages available that will automatically 'domify'
an object graph, but within Spring, you have complete flexibility to
create the DOM from your model in any way you choose. This prevents
the transformation of XML playing too great a part in the structure of
your model data which is a danger when using tools to manage the
domification process.

14.5.1.3. Convert the model data to XML

In order to create a DOM document from our list of words or any
other model data, we must subclass the (provided)
org.springframework.web.servlet.view.xslt.AbstractXsltView
class. In doing so, we must also typically implement the abstract method
createXsltSource(..) method. The first parameter passed
to this method is our model map. Here's the complete listing of the
HomePage class in our trivial word application:

A series of parameter name/value pairs can optionally be
defined by your subclass which will be added to the transformation
object. The parameter names must match those defined in your XSLT
template declared with
<xsl:param name="myParam">defaultValue</xsl:param>.
To specify the parameters, override the
getParameters() method of the
AbstractXsltView class and return a
Map of the name/value pairs. If your parameters
need to derive information from the current request, you can (from Spring version
1.1) override the
getParameters(HttpServletRequest request) method instead.

Unlike JSTL and Velocity, XSLT has relatively poor support for
locale based currency and date formatting. In recognition of the
fact, Spring provides a helper class that you can use from within
your createXsltSource(..) method(s) to get such
support. See the Javadocs for the
org.springframework.web.servlet.view.xslt.FormatHelper
class.

14.5.1.4. Defining the view properties

The views.properties file (or equivalent xml definition if
you're using an XML based view resolver as we did in the Velocity
examples above) looks like this for the one-view application that is
'My First Words':

Here, you can see how the view is tied in
with the HomePage class just written which handles the model
domification in the first property '.class'. The 'stylesheetLocation'
property points to the XSLT file which will handle the XML
transformation into HTML for us and the final property '.root' is the
name that will be used as the root of the XML document. This gets
passed to the HomePage class above in the second parameter to the
createXsltSource(..) method(s).

14.5.1.5. Document transformation

Finally, we have the XSLT code used for transforming the above
document. As shown in the above 'views.properties' file, the stylesheet is called
'home.xslt' and it lives in the war file in the
'WEB-INF/xsl' directory.

You will also need to ensure that an XML parser and an XSLT engine are available on the
classpath. JDK 1.4 provides them by default, and most J2EE containers
will also make them available by default, but it's a possible source of
errors to be aware of.

14.6. Document views (PDF/Excel)

14.6.1. Introduction

Returning an HTML page isn't always the best way for the user to
view the model output, and Spring makes it simple to generate a PDF
document or an Excel spreadsheet dynamically from the model data. The
document is the view and will be streamed from the server with the
correct content type to (hopefully) enable the client PC to run their
spreadsheet or PDF viewer application in response.

In order to use Excel views, you need to add the 'poi' library to
your classpath, and for PDF generation, the iText.jar. Both are included
in the main Spring distribution.

14.6.2. Configuration and setup

Document based views are handled in an almost identical fashion to
XSLT views, and the following sections build upon the previous one by
demonstrating how the same controller used in the XSLT example is
invoked to render the same model as both a PDF document and an Excel
spreadsheet (which can also be viewed or manipulated in Open
Office).

14.6.2.1. Document view definitions

Firstly, let's amend the views.properties file (or xml
equivalent) and add a simple view definition for both document types.
The entire file now looks like this with the XSLT view shown from
earlier..

If you want to start with a
template spreadsheet to add your model data to, specify the location
as the 'url' property in the view definition

14.6.2.2. Controller code

The controller code we'll use remains exactly the same from the
XSLT example earlier other than to change the name of the view to use.
Of course, you could be clever and have this selected based on a URL
parameter or some other logic - proof that Spring really is very good
at decoupling the views from the controllers!

14.6.2.3. Subclassing for Excel views

Exactly as we did for the XSLT example, we'll subclass suitable
abstract classes in order to implement custom behavior in generating
our output documents. For Excel, this involves writing a subclass of
org.springframework.web.servlet.view.document.AbstractExcelView
(for Excel files generated by POI)
or org.springframework.web.servlet.view.document.AbstractJExcelView
(for JExcelApi-generated Excel files).
and implementing the buildExcelDocument

Here's the complete listing for our POI Excel view which displays
the word list from the model map in consecutive rows of the first
column of a new spreadsheet..

Note the differences between the APIs. We've found that the
JExcelApi is somewhat more intuitive and furthermore, JExcelApi
has a bit better image-handling capabilities. There have been
memory problems with large Excel file when using JExcelApi however.

If you now amend the controller such that it returns
xl as the name of the view (return new
ModelAndView("xl", map);) and run your application again,
you should find that the Excel spreadsheet is created and downloaded
automatically when you request the same page as before.

14.6.2.4. Subclassing for PDF views

The PDF version of the word list is even simpler. This time, the
class extends
org.springframework.web.servlet.view.document.AbstractPdfView
and implements the buildPdfDocument() method as
follows..

Once again, amend the controller to return the
pdf view with a return new
ModelAndView("pdf", map); and reload the URL in your
application. This time a PDF document should appear listing each of
the words in the model map.

14.7. JasperReports

JasperReports (http://jasperreports.sourceforge.net)
is a powerful open-source reporting engine that supports the creation of report
designs using an easily understood XML file format. JasperReports is capable of
rendering reports output into four different formats: CSV, Excel, HTML and PDF.

14.7.1. Dependencies

Your application will need to include the latest release of
JasperReports, which at the time of writing was 0.6.1. JasperReports
itself depends on the following projects:

BeanShell

Commons BeanUtils

Commons Collections

Commons Digester

Commons Logging

iText

POI

JasperReports also requires a JAXP compliant XML parser.

14.7.2. Configuration

To configure JasperReports views in your Spring container configuration
you need to define a ViewResolver to map view
names to the appropriate view class depending on which format you want your
report rendered in.

14.7.2.1. Configuring the ViewResolver

Typically, you will use the ResourceBundleViewResolver
to map view names to view classes and files in a properties file.

Here we've configured an instance of the ResourceBundleViewResolver
class that will look for view mappings in the resource bundle with base name
views. (The content of this file is described in the next section.)

14.7.2.2. Configuring the Views

The Spring Framework contains five different View
implementations for JasperReports, four of which correspond to one of the four output
formats supported by JasperReports, and one that allows for the format to be determined at runtime:

Here you can see that the view with name simpleReport
is mapped to the JasperReportsPdfView class, causing the
output of this report to be rendered in PDF format. The url
property of the view is set to the location of the underlying report file.

14.7.2.3. About Report Files

JasperReports has two distinct types of report file: the design
file, which has a .jrxml extension, and the
compiled report file, which has a .jasper
extension. Typically, you use the JasperReports Ant task to compile
your .jrxml design file into a
.jasper file before deploying it into your
application. With the Spring Framework you can map either of these files to your
report file and the framework will take care of compiling the
.jrxml file on the fly for you. You should note
that after a .jrxml file is compiled by the Spring Framework,
the compiled report is cached for the lifetime of the application. To make
changes to the file you will need to restart your application.

14.7.2.4. Using JasperReportsMultiFormatView

The JasperReportsMultiFormatView allows for
report format to be specified at runtime. The actual rendering of the
report is delegated to one of the other JasperReports view classes -
the JasperReportsMultiFormatView class simply adds
a wrapper layer that allows for the exact implementation to be
specified at runtime.

The JasperReportsMultiFormatView class
introduces two concepts: the format key and the discriminator key. The
JasperReportsMultiFormatView class uses the mapping
key to lookup the actual view implementation class and uses the format
key to lookup up the mapping key. From a coding perspective you add an
entry to your model with the formay key as the key and the mapping key
as the value, for example:

In this example, the mapping key is determined from the
extension of the request URI and is added to the model under the
default format key: format. If you wish to use a
different format key then you can configure this using the
formatKey property of the
JasperReportsMultiFormatView class.

By default the following mapping key mappings are configured in
JasperReportsMultiFormatView:

Table 14.3. JasperReportsMultiFormatView Default Mapping Key Mappings

Mapping Key

View Class

csv

JasperReportsCsvView

html

JasperReportsHtmlView

pdf

JasperReportsPdfView

xls

JasperReportsXlsView

So in the example above a request to URI /foo/myReport.pdf
would be mapped to the JasperReportsPdfView class.
You can override the mapping key to view class mappings using the
formatMappings property of
JasperReportsMultiFormatView.

14.7.3. Populating the ModelAndView

In order to render your report correctly in the format you have
chosen, you must supply Spring with all of the data needed to populate
your report. For JasperReports this means you must pass in all report
parameters along with the report datasource. Report parameters are
simple name/value pairs and can be added be to the
Map for your model as you would add any name/value
pair.

When adding the datasource to the model you have two approaches to
choose from. The first approach is to add an instance of
JRDataSource or a Collection type to the
model Map under any arbitrary key. Spring will then
locate this object in the model and treat it as the report datasource.
For example, you may populate your model like so:

The second approach is to add the instance of
JRDataSource or Collection under a
specific key and then configure this key using the
reportDataKey property of the view class. In both
cases Spring will instances of Collection in a
JRBeanCollectionDataSource instance. For example:

Be aware that when using the first approach, Spring will use the
first instance of JRDataSource or
Collection that it encounters. If you need to place
multiple instances of JRDataSource or
Collection into the model then you need to use the
second approach.

14.7.4. Working with Sub-Reports

JasperReports provides support for embedded sub-reports within
your master report files. There are a wide variety of mechanisms for
including sub-reports in your report files. The easiest way is to hard
code the report path and the SQL query for the sub report into your
design files. The drawback of this approach is obvious - the values are
hard-coded into your report files reducing reusability and making it
harder to modify and update report designs. To overcome this you can
configure sub-reports declaratively and you can include additional data
for these sub-reports directly from your controllers.

14.7.4.1. Configuring Sub-Report Files

To control which sub-report files are included in a master
report using Spring, your report file must be configured to accept
sub-reports from an external source. To do this you declare a
parameter in your report file like so:

This defines a master report file that
expects the sub-report to be passed in as an instance of
net.sf.jasperreports.engine.JasperReports under the
parameter ProductsSubReport. When configuring your
Jasper view class, you can instruct Spring to load a report file and
pass into the JasperReports engine as a sub-report using the
subReportUrls property:

Here, the key of the Map
corresponds to the name of the sub-report parameter in th report
design file, and the entry is the URL of the report file. Spring will
load this report file, compiling it if necessary, and will pass into
the JasperReports engine under the given key.

14.7.4.2. Configuring Sub-Report Data Sources

This step is entirely optional when using Spring configure your
sub-reports. If you wish, you can still configure the data source for
your sub-reports using static queries. However, if you want Spring to
convert data returned in your ModelAndView into
instances of JRDataSource then you need to specify
which of the parameters in your ModelAndView Spring
should convert. To do this configure the list of parameter names using
the subReportDataKeys property of the your chosen
view class:

<property name="subReportDataKeys"
value="SubReportData"/>

Here, the key you supply MUST
correspond to both the key used in your ModelAndView
and the key used in your report design file.

14.7.5. Configuring Exporter Parameters

If you have special requirements for exporter configuration -
perhaps you want a specific page size for your PDF report, then you can
configure these exporter parameters declaratively in your Spring
configuration file using the exporterParameters
property of the view class. The exporterParameters
property is typed as Map and in your configuration
the key of an entry should be the fully-qualified name of a static field
that contains the exporter parameter definition and the value of an
entry should be the value you want to assign to the parameter. An
example of this is shown below:

Here you can see that the JasperReportsHtmlView is
being configured with an exporter parameter for
net.sf.jasperreports.engine.export.JRHtmlExporterParameter.HTML_FOOTER
which will output a footer in the resulting HTML.